Fuel without Oxygen: Understanding Creatine

How does the creatine phosphate system allow for muscles to "breathe"?

By Michael Ormsbee, PhDFlorida State University
Edited by Kate Findley and proofread by Angela Shoemaker, Wondrium Daily

You may be familiar with creatine supplements, but our body also produces creatine naturally using a combination of amino acids. It is part of a system that helped our ancestors escape from wild beasts, and today it assists in climbing flights of stairs and lifting heavy weights. Michael Ormsbee, Ph.D., discusses the benefits of this anaerobic system.

image of creatine molecular structure written on paper with supplements
The creatine phosphate system assists muscles by providing oxygen during short bursts of anaerobic exercise like climbing stairs and lifting weights. Image by: Danijela Maksimovic / Shutterstock

Creatine Phosphate System

Three energy-producing systems—the creatine phosphate, glycolytic, and oxidative systems—operate in conjunction with adenosine triphosphate (ATP) to keep our body running. All of these systems work to provide us energy, but one system is typically used more than the others during different exercise and rest scenarios.

The first energy system—the creatine phosphate system—works hardest for us during maximal intensity exercise such as running fast for a few seconds or lifting a heavy object or weight. In this system, you will create ATP first by combining a phosphate with stored creatine to form creatine phosphate. 

Then, the enzyme creatine kinase breaks the phosphate off of creatine phosphate and allows it to combine with adenosine diphosphate (ADP). This forms more ATP and free creatine. The process is anaerobic; it occurs without oxygen.

How Anaerobic Exercise Works

You are still breathing oxygen at the normal 21 percent that exists in the atmosphere, but these energy-creating processes are called anaerobic, meaning without oxygen, because ATP can be produced without the presence of oxygen in the cells.

Think about when you run up a flight of stairs and you’re out of breath. This would be a lack of oxygen in your cells, but the ability to get up the stairs, despite the lack of oxygen, is provided primarily by the creatine phosphate system. Thus, the term anaerobic also tells us that this system is one that will work when you are doing intense activity or exercise. 

The creatine phosphate energy system works quickly, but it does not last for long—about 30 seconds is all you’ll get, depending on your fitness level. However, it is the most rapid method to regenerate ATP.

Just because the creatine phosphate system is short-lived does not mean it isn’t valuable—it is extremely useful to us. Think about any time you need to do a very quick action—jump out of the way of something, run quickly for a few steps, or lift something heavy. 

All of these require the creatine phosphate system. If you’re really active, this system also assists in giving quick, hard efforts when you need to run up a hill, pass someone in a race, or lift heavy weights.

Most exercise physiology textbooks indicate that our body only draws energy from this system for 30 seconds before taking from other systems. However, the creatine phosphate system can be used at nearly any point of activity and repeated after a short break, even though the energy production only lasts for a few seconds. 

Creatine Stores

We are able to repeatedly draw from our creatine system because of something called the size principle, which states that you can recruit muscles for activity in an orderly and efficient fashion, from smallest to largest. Some muscles will burn through their stored creatine phosphate, but other larger muscle fibers will keep it until it is needed for a burst of high-intensity activity.

Interestingly, creatine stores are useful for everyone, not just power and strength athletes. Also, although creatine is made naturally in our bodies, we do get some from the foods we eat, mostly from meat. So yes, vegetarians and vegans will likely have less stored creatine. 

However, creatine can also be consumed as a supplement. In fact, it is the most widely studied sports nutrition supplement on the planet, and now research is showing the benefits of creatine supplement use for just about every population: young, old, healthy, and diseased. 

This article was edited by Kate Findley, Writer for Wondrium Daily, and proofread by Angela Shoemaker, Proofreader and Copy Editor for Wondrium Daily.
Dr. Ormsbee is an Associate Professor in the Department of Nutrition, Food, and Exercise Sciences and Interim Director of the Institute of Sports Sciences and Medicine in the College of Human Sciences at Florida State University.

Michael Ormsbee is an Associate Professor in the Department of Nutrition, Food, and Exercise Sciences and Interim Director of the Institute of Sports Sciences and Medicine in the College of Human Sciences at Florida State University. He received his MS in Exercise Physiology from South Dakota State University and his PhD in Bioenergetics from East Carolina University.